Dinosaurs and… Quantum Mechanics?

In the movie, The Lost World: Jurassic Park, one of the characters references a scientific principle that is not very well known to the public. That is the Heisenberg Uncertainty Principle. To put it in context, this principle is referenced when our main characters first arrive on the island of dinosaurs. One of the characters, Sarah Harding, insists that they must observe the animals without interfering with them. Another character, Ian Malcolm, responds by saying that the Heisenberg Uncertainty Principle states that the act of observing something necessarily interacts with that thing, therefore it is impossible to observe without interacting.

Strangely enough, for a movie about dinosaurs, where one might expect paleontology to be a prevalent topic, the Heisenberg Uncertainty Principle actually applies to quantum physics. Quantum physics deals with subatomic physics. It is called quantum physics because, while our ordinary experience is that physical properties exist on a continuous spectrum, at the subatomic level, things occur in discrete steps, or quanta. For example, suppose that there is a ball flying through the air. We can calculate the energy of the ball due to its motion. We refer to this as kinetic energy. The kinetic energy of an object is calculated by

KE=1/2mv²,

where KE is the kinetic energy, m is the mass of the object, and v is the velocity (or speed) of the object. While the mass of the ball is fixed, the velocity can be anything we want, depending on how hard it is thrown. This includes any fractional speed. Say that the speed is 12 feet per second. There is nothing preventing us from giving it a speed of 12.1, or 12.01, or 12.001, or 12.0001 feet per second, and so on. This is because the velocity exists on a spectrum: there are no specific “bundles” of velocity that force the velocity to increase by specific, incremental steps. Furthermore, since the kinetic energy is depended upon velocity, the kinetic energy also exists as a spectrum with no discrete steps.

However, things are different at the quantum level. Now, energy is acquired in specific bundles. Take the following illustration, for example. Both images show a hydrogen atom. There is a proton in the middle (the blue circle) with an electron (the black circle) orbiting around it. How close the orbit of the electron is to the proton depends on the energy of the electron. Thus, the electron in the atom on the left has less energy than the electron on the right.

Now, if we apply our understanding of physics to quantum physics, we might expect that the orbit of the electron can be anywhere that we want. All we have to do is increase the energy of the electron a little bit, and the orbit will expand slightly. Thus, we might expect that the electron can orbit at a distance between the two orbits illustrated above. Makes sense, right? Well, it doesn’t work that way. Instead, the electron will only orbit at one of the two levels seen above. It will either have enough energy to orbit like the atom on the left, or enough energy to orbit like the atom on the right. There is no in between. Put another way, the electron either has one of two energy states, rather than any amount of energy that we choose. This is what is meant by quantum mechanics: things exist at discrete steps rather than along a continuous spectrum.

That is a long explanation for a very fundamental concept in quantum mechanics, but it is important to know how different quantum mechanics is compared to our everyday experience. It also helps set up our understanding of the Heisenberg Uncertainty Principle, which states that it is impossible to detect the position and velocity of an electron simultaneously. To understand why this is the case, let us again think of a ball traveling through the air. How can we detect the position and velocity of the ball? For one thing, we need to understand that we will typically detect the ball by electromagnetic radiation. We can watch the ball travel through the air, which occurs because light (a type of electromagnetic radiation) bounces off of the ball and to our eyes. While seeing the ball may allow us to know its position, what about its speed? We can use a speed gun, which reflects radio waves (another form of electromagnetic radiation) off of the ball, detects the waves, and interprets it as speed. In both cases, does the light or the radio waves interfere with the ball? No, it does not. We can, theoretically, set up a speed gun to read the ball’s speed at a specific point in its flight, so it is quite possible to detect the position and speed of a ball at once.

What about an electron? We can still use electromagnetic radiation to detect the velocity or speed of an electron. However, we run into a problem: whatever radiation is used; light, radio waves, or something else; will interfere with the electron and change its position and velocity. Electromagnetic radiation is a form of energy. When such energy strikes a ball, we can “dial back” the energy to such a small level that it does not interfere with the ball. However, energy comes in discrete bundles in quantum mechanics, so any energy used to detect the position of an electron will be sufficient to knock it off course, thus changing its position, or speed it up, thus changing its velocity. That is the basis for the Heisenberg Uncertainty Principle: we cannot detect the position and velocity of an electron simultaneously because any attempt to do so will interfere with the electron and throw it off course.

As a final thing to note about the Heisenberg Uncertainty Principle, note that because it defines a relationship between velocity and position of an electron, it actually helps physicists as they observe electrons. True, they may not be able to find the position and velocity at the same time, but they know the limit of their ability to detect these quantities, and they are actually able to treat it like a trade-off: they can be certain of its velocity at the expense of knowing its position, or be certain of its position at the expense of knowing its velocity. Despite the name “uncertainty” in the title of the principle, it actually helps makes things more precise, or at least, define a limit of precision.

Let us now return to The Lost World: Jurassic Park. It is my opinion that Ian Malcolm used the Heisenberg Uncertainty Principle improperly. First of all, while the principle is related to “can’t observe without interfering,” it is much more specific than that. The Heisenberg Uncertainty Principle was not formulated as a general decree that any observation interferes with any thing being observed: it was limited to electrons (though today, the principle has been expanded to include other objects at the quantum level). Second, the Heisenberg Uncertainty Principle is defined for quantum mechanics: it is not necessarily applicable to Newtonian (“normal”) physics. Thus, while Ian Malcolm’s statement may be an interesting pop culture reference to a little known principle, it is, unfortunately, not the best example of said principle.

Thoughts from Steven